This kind of valve is generally used in hydraulic systems for leakage-free blocking of conduits and the like, often to eliminate "load sinking" in different types of hydraulic cylinders. This load sinking occurs when a load, work implement or the like, which is kept raised at a certain level by such a cylinder, slowly sinks or in some other way alter its position due to hydraulic liquid leaking out from the pressure side of the cylinder because of internal leakage in the hydraulic system, e.g. at the cylinder operating valve, in spite of this value being in its neutral position and thus closed.
The valve types which up to now have been used to eliminate load sinking, e.g. pilot-controlled non-return valves or so-called overcentre valves have characteristics intrinsic with their functional principle such that they become unsuitable for their purpose in certain cases. Amongst other things, such a valve can have a flow resistance which is so large that the hydaulic cylinder is given a reduced maximum working speed, and furthermore, it is not possible to use these valve types without considerable complications for single acting hydraulic cylinders, so called telescopic cylinders.
The invention thus has the object of providing a holding valve of a kind in question, which can be used in all cases where leakagefree blocking, or holding, in a hydraulic system is desired without the system otherwise being affected, and without any extensive modification of the system being required. The object is achieved, and a hydraulic holding valve is provided in which the disadvantages indicated above and associated with earlier, similar valves have been obviated, by the valve in accordance with the invention having been given the characterizing features disclosed in claim 1.